Some observations on the growth of rutile single crystals using the optical floating zone method

Rutile single-crystal rods of approximately 5 mm diameter and up to 50 mm in length have been grown by the optical floating zone method using a variety of growth rates, rotation rates, oxygen pressures and molten zone temperatures. The crystals were characterised using both polarised optical microscopy and X-ray Laue techniques. The best quality crystals were prepared when neither the growing crystal nor the feed rod were rotated during crystal growth. When rotation was employed, this was found to introduce sub-grain boundaries in crystals when the linear growth rate was low, or bubble inclusions when the linear rate was high. The use of lower molten zone temperatures was found to give pale-yellow crystals, while crystals grown using higher molten zone temperatures tended to be blue in colour. Variation of oxygen pressure in the growth chamber (between 1×105 and 5×105 Pa) was found to have little effect on either crystal quality or colour.